Hi ! You have not mentioned about your age and sex and if there was any history of trauma you remember. Sometimes unnoticed trivial trauma might give rise to small hematoma
, which may give rise swelling with such characteistics.
In young persons, an entity named Tietz syndrome may cause similar symptoms and signs. In both the cases, you may take some anti inflammatory drugs on consultation with your physician which may give you relief. In case it is increasing without any relief, then you are advised to get reviewed by an orthopaedic surgeon/general surgeon
who may go for some special investigations to exclude other causes of your symptoms.
Wishing you an early recovery.